h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Hi Gnomon, I love the article.
If everything was molten does that mean that the rock is a mix of all sorts of different things in a sort of soup that then, as it cools, congeals? Would that be like a vegetable soup with all sorts of different chunks in it or is it more like a tomato soup with pretty much the same constituents wherever you dip your spoon?

I may get onto a cheese question later on...

I have another question. Why is the moon slowly moving away?

And if the answer can be expressed in terms of soup and cheese, that would be oddly impressive.

Hi Vestboy and Baron Grim. Sorry for not getting back to you earlier, but I was on holidays in Greece and I can't compose long answers on my mobile phone.

When the moon formed first, it would have been fully liquid, at a few thousand degrees. Then as it cooled, some things would have sunk and other things floated, so it would have ended up with different elements at different places. The same sort of thing happened in the Earth where the iron sank to the centre. So probably more like a chunky vegetable soup than a tomato one.

I don't fully understand why the Moon is moving away from the Earth. I've been told that the Moon's gravity pulls the oceans around the Earth, but this takes energy away from the Moon. As the Moon loses kinetic energy and slows down, it moves outward to a position where its speed is enough to keep it in orbit, so it spirals outwards very, very slowly.

I don't understand that, but maybe it makes some sense to you. I would think, for example, that if a spaceship was in orbit around the earth and it slowed down, it would no longer have the speed to stay up, so it would fall towards the earth. I don't know why the moon would in the same situation move away. Someday I'll try and work out the mathematics.

I knew you were on holiday and wasn't anxiously waiting for an answer.


I can't say I'm competent at orbital mechanics, but I think I understand the basics. In other words, I know enough to easily get it completely wrong in interesting ways.

I understand that objects in LEO typically experience drag from the thin atmosphere and other effects. Without the occasional correctional thrust the ISS would fall back to Earth like Skylab did. Those "other reasons" are various and strange.

For instance, before I started working for NASA I was fascinated by the first Tethered Satellite System (TSS) mision, STS-46. http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/archives/sts-46.html
Briefly, the were going to extend a small satellite out from the Shuttle 20km to study the feasibility of such a system to, among other things, generate electricity as the conductive tether passes perpendicularly through the Earth's magnetic field. I've been interested in tethered satellites since reading about Arthur C. Clarke's skyhook idea.

Even though they never got the TSS fully deployed it did generate a significant voltage and amperage. Which lead me to consider my physics lessons and realize that this electricity is being generated at a cost to their orbital momentum through a "drag" from Electro-Motive Force (EMF). In essence, this was a convoluted method of converting chemical energy into electrical energy as they would need to reboost to make up for the retrograde EMF. This was never mentioned in the popular press.

Anyways... here's my wild theory about the moon slowly getting farther away.

Could it possibly be significantly affected by the Earth losing mass from lighter gases, like Helium, being eroded away by solar wind?

I suspect there are much more significant factors involved, I just don't know what they are.

I don't think it is to do with the mass of the Earth changing. If anything, the Earth is getting heavier as thousands of meteorites strike it every day. It's a feature of orbital mechanics, and I will need to investigate it.

Hmm... Synchronicity.


http://www.abc.net.au/news/2014-09-21/japanese-construction-giants-promise-space-elevator-by-2050/5756206

Interesting. I said in the space elevator entry A1904249 that they would probably use nanotubes.

I love reading this stuff but most goes right over my head, but not all. Talking of nanotubes today they announced that a British science team have used them to create the blackest object known to man (and woman) and surprisingly it's not the ring around my bath.

Yes. They compared it to the ISO standard, Dick Cheney's heart, kept in a jar at Bethesda Naval Hospital.

Further study shows that the moon is gaining energy due to its tidal action on the earth, rather than losing it. The extra energy causes it to move into a higher orbit.

Don't understand yet why it is gaining energy.

I love it when the seemingly simple things turn out to be quite complicated after all.


My favorite example is this: "Magnets; how do they work?"

http://www.youtube.com/watch?v=MO0r930Sn_8

... and he didn't explain what horse shoes have to do with it, either.